A wood plastic composite (WPC) is a term which refers to a composite containing wood in any form, combined with either thermoplastics (which can be re-melted) or thermoset plastics (which cannot be re-melted once set). Thermoplastics include polyethylene and polypropylene which are used in numerous non-structural applications such as bottles and containers. Thermoset plastics are formed from resins such as polyester and epoxy. Bakelite was the first type of thermoset plastic (dating back to 1900), and was composed of wood flour and phenol-formaldehyde (Clemens, 2002). Most WPCs currently on the market are made from thermoplastics, in particular High Density Polyethylene (HDPE). The nature of the wood content is either wood flour or sawdust. At first inspection, the combination of wood fibre and a thermoplastic does not seem promising. Wood fibres (eg in the form of sawdust) are short, tend to absorb moisture and are not strong when compared with either the glass or carbon fibres used in FRPs. Thermoplastics are much weaker than thermosetting resins, soften with increasing temperature and creep under load. However, WPCs combine inexpensive or waste raw materials, and the production process for low technology sections such as decking planks, fencing and handrails is relatively simple. Particularly in the USA, WPCs have been hugely successful because they offer advantages of durability and lower maintenance over natural wood. Solid recycled plastic lumber (RPL), is usually made from waste plastics without any wood or fibre element (and is therefore is not a composite), also competes in this non-structural role. Polyvinyl Chloride (PVCu) is another type of plastic which has familiar application for window frames, doors and fascia panels.
Around 8.3 million tonnes of plastics per year are used in construction in Western Europe. Building and construction is the second most important market for plastics, representing a volume of 23 %, and only coming second to packaging applications. Applications include pipes, tanks, floor covering, insulation, window frames and doors. PVCu in particular is used for skirting boards, window frames and doors, cladding and fascia panels. Recently FRPs have begun to be used in place of PVCu for window frames, doors and weatherboarding, in the same way that PVCu previously displaced timber from much of the market. Development of plastics and composites as woodalternatives could have a negative effect on the potential for solid UK timber, in particular the development of “spruce for joinery”, and UK timber for bridges, piles, and also cladding. Plastics are already being used instead of low-grade timber for applications such as fencing and pallets.